Muzzleloaders are a class of firearms in which the propellant charge and bullet are separately loaded into the barrel immediately prior to firing. Unlike modern breech loaded firearms where the bullet, propellant charge and primer are loaded as prepackaged cartridges, conventional muzzleloaders are loaded by feeding a propellant charge through the muzzle of the barrel before ramming a bullet down the barrel with a ramrod until the bullet is seated against the propellant charge at the breech end of the barrel. A primer is then fitted to the exterior end of a hole in the breech end of the barrel. The primer is then struck by an internal inline firing pin or an external hammer to ignite the propellant charge through the hole in the breech end of the barrel to create propellant gases for propelling the bullet.
The loading process of muzzleloaders creates issues unique to muzzleloaders. Specifically, the muzzleloader loading process requires that, unlike conventional breech loaded firearms, the bullet travel through the barrel twice, once during loading and once during firing. The tight fit of the bullet to the barrel can create substantial friction as the bullet travels through the barrel and is etched by the barrel rifling. During firing, the expanding propellant gases can overcome the frictional forces to propel the bullet through the barrel. However, during loading, the user must overcome the frictional force by applying an axial force to the bullet with the ramrod until the bullet is seated against the propellant charge. The friction between the bullet and the barrel can complicate the determination as to whether the bullet has been pushed far enough down the barrel during loading and is properly seated against the propellant charge. The relative position of the bullet to the propellant charge changes the pressurization of the barrel behind the bullet from the ignited propellant gases impacting the ballistic performance and potentially creating a substantial safety risk.
A recent trend in muzzleloading is placing an undersized bullet within a polymer sabot in a barrel sized for a larger caliber bullet. The undersized bullet body has a higher muzzle velocity than the larger caliber bullet providing improved ballistic characteristics. The sabot is sized to approximate the inner diameter of the barrel such that the sabot tightly seals against the barrel to efficiently propel the bullet and engage the rifling of the barrel to impart spin to the bullet. The sabot typically comprises a plurality of pedals or other unfurling element that unfurl from the bullet to separate the sabot from the bullet as the bullet leaves the muzzle to disengage from the bullet. While the sabot substantially improves the ballistic performance of the muzzleloader, the polymer sabot can be damaged or deformed by passing through the barrel and engaging the rifling twice. The deformation of the sabot or damage to the sabot can cause the sabot to release the bullet prematurely or impart a wobble to the bullet.
A similar concern with muzzleloaders is that the slower burning propellant required by muzzleloaders often foul the barrel with unconsumed residue requiring frequent cleaning of the barrel. The fouling often occurs so quickly that the barrel must be cleaned after every shot. The fouling can also interfere with the operation the sabot causing the sabot to begin to unfurl from the bullet prematurely within the barrel or break up within the barrel. In addition to contributing the fouling of the barrel, the deformation or damage to the sabot can impart wobble into the bullet or otherwise impact the ballistic performance of the bullet.
An additional complication is that the actual inner diameter of the barrel for given caliber can vary from manufacturer to manufacturer. A 50 caliber barrel can have an actual inner diameter ranging from 0.497 to 0.505 inches depending on the manufacturer. Similarly, a 45 caliber bullet saboted for use in a 50 caliber barrel can have an outer diameter varying from 0.450 to 0.452 inches, which in turn changes the outer diameter of the sabot the bullet is seated within. Although the variance is relatively small, the variance in tolerances between the inner diameter of the barrel and the outer diameter of the sabot can result in substantially increased friction between the cupped bullet and the barrel, which can cause the bullet to become stuck within the barrel during firing or loading. Similarly, an improper fit between the barrel and an undersized sabot can create an inefficient seal between the sabot and the barrel allowing gases to escape around the bullet during firing. Accordingly, if the sabot-bullet pairing is not properly selected, the effectiveness of the muzzleloader can be substantially impacted.
A similar variability in muzzleloaders not present in cartridge based firearms is the variability of the size of the propellant charge. Unlike cartridge firearms where a cartridge is preloaded with a bullet and premeasured quantity of propellant is loaded into the firearm for firing, the bullet and propellant charge are combined within the firearm for firing. Accordingly, the muzzleloader operator can select the optimal bullet, propellant type and quantity combination for each shot, which is particularly advantageous given the long reloading time for muzzleloaders. While the variability of the bullet—propellant charge combination allows for an optimized shot, varying the bullet and in particular the propellant and quantity of propellant can significantly change the appropriate seating depth of the bullet. With loose or powdered propellant such as black powder, the amount of propellant is often varied between 80 and 120 volumetric grains. Similarly, propellants are often formed into cylindrical pellets that are stacked end-to-end within the barrel to form the propellant charges. The pellets are typically each about 1 cm in length and loaded in 1 to 3 pellet groups causing an even greater variation in the seating depth.
A common approach to determining whether a bullet has been properly seated involves marking the ramrod with a visual indicator that aligns with the muzzle of the barrel when the end of the ramrod is at the appropriate depth with the barrel. The visual indicator is typically marked by loading the propellant charge and ramming a test bullet through the barrel. Once the user is certain that the bullet is properly seated against the propellant charge, the corresponding portion of the ramrod at the muzzle is marked. Although this approach is relatively easy to implement and widely used, the visual indicator approach detracts from the primary advantages of muzzleloaders. As the visual indicator approach is set based on a particular propellant charge and bullet combination, a variation in the propellant charge that changes the dimensions of the propellant charge can render the visual indicator at best useless or at worse a safety risk giving a false appearance of a properly seated bullet.
As discussed above, the fouling can interfere with the safe operation of the muzzleloader as well as the ballistic performance of the bullet. While firing the muzzleloader can be comparatively safer method of unloading the bullet, the muzzleloader must often be cleaned after each firing. In a hunting situation where the muzzleloader may be fired several times to unload the muzzleloader for transport, the barrel may require cleaning, which can be difficult in the field.
A current approach to addressing the reloading problem is replacing the closed breech end of the muzzleloader barrel with a screw-in, removable breech plug. The breech plug is removable from the breech end of the muzzle to remove the propellant charge from behind the bullet rather than attempting the remove the bullet from the muzzle end of the barrel. While the approach is effective in safely separating the propellant charge from the bullet, a common problem with removable breech plugs is seizing of the breech plug within the barrel. The rapid temperature changes during firing as well as the corrosive nature of many of the propellants can result in seizing of the corresponding threads of the breech plug and the barrel. If not carefully maintained, the breech plug will become difficult to remove to efficiently unload the muzzleloader.
A related concern is that the performance of the hygroscopic propellant itself can be easily and often detrimentally impacted by the environmental conditions in which the propellant is stored. The sensitivity of the propellant can often result in “hang fires” where the ignition of the propellant charge is delayed or the propellant charge fails to ignite altogether. Hang fires are frequent occurrences and create a substantial risk for the user. The conventional approach to dealing with a hang fire is to point the muzzleloader in a safe direction until the muzzleloader fires or until sufficient time has passed to reasonably assume that the propellant charge failed to ignite altogether. The unloading process through the muzzle of the muzzleloader is particularly dangerous in hang fire situations as the propellant charge may ignite during the actual unloading process. Similarly, unloading through a breech plug can similarly be dangerous as the propellant charge may ignite as the breech plug is removed.
Another safety concern unique to muzzleloaders is an undersized or oversized propellant charge. Unlike cartridge firearms where the amount of propellant loaded for each shot is limited by the internal volume of the cartridge, the amount of propellant loaded for each shot in muzzleloaders is only limited by the length of the barrel. While measures are often used to provide a constant quantity of propellant for each propellant charge, the measures can be difficult to use in the field or in low light situation when hunting often occurs. Similarly, propellant can be formed into the pre-sized pellets that can be loaded one at a time until the appropriate amount of propellant is loaded. As with the measure, loading the appropriate number of pellets can be challenging in the field or in low light situations.
The fit between the barrel and bullet can impact the ballistic performance of the muzzleloader. However, tightly fitting the bullet to the barrel can make properly seating of the bullet against the propellant charge and determining the position of the bullet within the barrel during loading difficult. Accordingly, there is a need for efficiently loading and seating a muzzleloader bullet within the barrel while tightly fitting the bullet to the walls and rifling of the barrel.